System and method for adapting a transport stream for transmission

Abstract

An ASI transport stream is processed in a way that allows the use of an RF wireless link to connect a distribution network to a transmitter in a single-frequency network. Null packets are disguised by changing the PID value of each null packet to a PID value that has been arranged to designate null packets. Each packet that contains a PCR stamp is amended to hide the presence of the PCR stamp. As a result, none of the packets in the transport stream are recognized, by elements of the RF link, as a null packet or as a packet containing a PCR stamp. Accordingly, such packets are considered, by elements of the RF link, to be packets carrying payload. Advantageously, then, packets that would normally be removed or modified by elements of the RF link pass through without being removed or modified.

1 . A method of adapting a transport stream for transmission to transmitters in a single-frequency network, said method comprising:
 receiving a packet, said packet having a header, said header having a field for a packet identifier;   determining whether said packet is a null packet;   if said packet is a null packet, amending said header to provide, in said field for said packet identifier, a predetermined value, thereby generating an amended packet, where said predetermined value is distinct from a value associated with null packets in a standard; and   transmitting said amended packet.   
   
   
       2 . The method of  claim 1  wherein said determining whether said packet is a null packet comprises considering as a null packet any packet having said value associated with null packets in said standard in said field for said packet identifier. 
   
   
       3 . The method of  claim 1  further comprising, if said packet is a null packet, amending said packet so that said packet includes a plurality of specifically coded bytes. 
   
   
       4 . The method of  claim 1  further comprising, if said packet is not a null packet:
 determining whether said packet carries a program clock reference stamp;   if said packet carries a program clock reference stamp, amending said header to disguise presence of said program clock reference stamp, thereby generating an amended packet; and   transmitting said amended packet.   
   
   
       5 . The method of  claim 4  wherein said determining whether said packet carries a program clock reference stamp comprises:
 determining whether said packet has an adaptation field; and   if said packet has an adaptation field, determining whether a flag, in a predetermined location in said adaptation field, is set to indicate that a program clock reference stamp is present.   
   
   
       6 . The method of  claim 5  wherein said amending said header to disguise presence of said program clock reference stamp comprises amending said header to disguise presence of said adaptation field. 
   
   
       7 . A headend in a single-frequency network comprising:
 an adapter adapted to:
 receive a packet, said packet having a header, said header having a field for a packet identifier; 
 determine whether said packet is a null packet; 
 amend said header to provide, in said field for said packet identifier, a predetermined value, thereby generating an amended packet, where said predetermined value is distinct from a value associated with null packets in a standard; and 
 transmit said amended packet. 
   
   
   
       8 . A computer readable medium containing computer-executable instructions that, when performed by processor in an adapter in a headend of a single-frequency network, cause said processor to:
 receive a packet, said packet having a header, said header having a field for a packet identifier;   determine whether said packet is a null packet;   amend said header to provide, in said field for said packet identifier, a predetermined value, thereby generating an amended packet, where said predetermined value is distinct from a value associated with null packets in a standard; and   transmit said amended packet.   
   
   
       9 . A method of receiving, at a transmitter in a single-frequency network, a transport stream adapted for transmission to said transmitter, said method comprising:
 receiving a packet, said packet having a header, said header having a field for a packet identifier;   determining whether said packet is a null packet;   if said packet is a null packet, amending said header to provide, in said field for said packet identifier, a value associated with null packets in a standard, thereby generating an amended packet; and   transmitting said amended packet.   
   
   
       10 . The method of  claim 9  wherein said determining whether said packet is a null packet comprises determining whether a value in said field for said packet identifier is equivalent to a predetermined value for identifying null packets, where said predetermined value is distinct from a value associated with null packets in a standard. 
   
   
       11 . The method of  claim 10  wherein said determining whether said packet is a null packet further comprises determining whether said packet includes a plurality of specifically coded bytes. 
   
   
       12 . The method of  claim 9  further comprising, if said packet is not a null packet,
 determining whether said packet disguises presence of a program clock reference stamp;   if said packet disguises presence of a program clock reference stamp, amending said header to allow presence of said program clock reference stamp to be determined, thereby generating an amended packet; and   transmitting said amended packet.   
   
   
       13 . The method of  claim 12  wherein said determining whether said packet disguises presence of a program clock reference stamp comprises determining whether said packet disguises presence of an adaptation field. 
   
   
       14 . The method of  claim 13  wherein said amending said header to allow presence of said program clock reference stamp to be determined comprises amending said header to indicate presence of said adaptation field. 
   
   
       15 . A transmitter in a single-frequency network comprising:
 an adapter adapted to:
 receive a packet, said packet having a header, said header having a field for a packet identifier; 
 determine whether said packet is a null packet; 
 amend said header to provide, in said field for said packet identifier, a value associated with null packets in a standard, thereby generating an amended packet; and 
 transmit said amended packet 
   
   
   
       16 . A computer readable medium containing computer-executable instructions that, when performed by processor in an adapter in a transmitter in a single-frequency network, cause said processor to:
 receive a packet, said packet having a header, said header having a field for a packet identifier;   determine whether said packet is a null packet;   amend said header to provide, in said field for said packet identifier, a value associated with null packets in a standard, thereby generating an amended packet; and   transmit said amended packet.